Japanese Unexamined Patent Publication No. 2017-089587 discloses to inject water into an intake passage of an internal combustion engine and use the latent heat of vaporization of the water to cool the air before flowing into a combustion chamber. Further, it discloses to keep the unevaporated water from ending up flowing into a combustion chamber together with the air by controlling the amount of water injected into the intake passage so that the amount of moisture in the air before flowing into the combustion chamber becomes the saturated steam amount or less.